This is the National phase Application of PCT/EP99/02397, field Apr. 8, 1999.
This invention relates to a process for the production of long-chain polyether polyols without working up.
Polyether polyols are obtainable by polyaddition of alkylene oxides, such as for example ethylene oxide, propylene oxide, butylene oxide, onto compounds containing active hydrogen atoms, such as alcohols, amines, acid amides, phenols, and are used inter alia for the production of polyurethane plastics, surfactants and lubricants. Polyaddition of epoxides onto starter compounds is conventionally performed industrially by alkali metal catalysis. The predominantly used alkali metal catalysts are alkali metal hydroxides. Disadvantages of alkali metal hydroxide catalysed polyether polyol production are primarily the elaborate working up of the product due to neutralisation of the alkaline polymer (c.f. for example U.S. Pat. No. 3,715,402, U.S. Pat. No. 4,430,490, U.S. Pat. No. 4,507,475 and U.S. Pat. No. 4,137,398) and the base-catalysed rearrangement of epoxides, for example propylene oxide, which proceeds as a secondary reaction, to yield allyl or propenyl alcohols, which give rise to monofunctional polyethers having a terminal double bond, which are known as monools.
One method known for the reduction of the monool content in the polyether polyols is to use double metal cyanide (DMC) complex compounds as catalysts for the polyaddition of epoxides onto starter compounds (c.f. for example U.S. Pat. No. 3,404,109, U.S. Pat. No. 3,829,505, U.S. Pat. No. 3,941,849 and U.S. Pat. No. 5,158,922). The polyether polyols obtained in this manner may be processed to yield high grade polyurethanes (for example elastomers, foams, coatings).
EP 700 949, EP 761 708, WO 97/40086 and DE-A 197 45 120.9, 197 57 574.9 and 198 102 269.0 disclose improved DMC catalysts which allow a further reduction in the fraction of monofunctional polyethers having terminal double bonds in the production of polyether polyols. The improved DMC catalysts are extraordinarily highly active and allow the production of polyether polyols at such low catalyst usage rates (25 ppm or below) that it is no longer necessary to separate the catalyst from the polyol (c.f. for example page 5, lines 24-29 in EP 700 949).
One disadvantage of using DMC catalysts for the production of polyether polyols is that these catalysts usually require an induction period. Unlike alkali metal catalysts, DMC catalysts do not start epoxide polymerisation immediately once the epoxide and starter compound have been added to the catalyst. The DMC catalyst must first be activated by a small quantity of epoxide. Induction periods are typically of a duration of some minutes to several hours.
Another disadvantage is that conventional, low molecular weight starter compounds for alkali metal catalysed polyether polyol synthesis, such as for example propylene glycol, glycerol or trimethylolpropane, cannot be alkoxylated with DMC catalysts. DMC catalysts thus require the use of oligomeric, alkoxylated starter compounds (for example a propoxylated propylene glycol or glycerol) having molecular weights of above 200, which have previously been obtained from the above-stated low molecular weight starters by, for example, conventional alkali metal catalysis (for example KOH catalysis) and subsequent elaborate working up by neutralisation, filtration and dehydration. Problematically, even very small residual quantities of alkali metal catalyst in the alkoxylated starter compounds can deactivate the DMC catalyst, such that a further additional, time-consuming working up stage (for example treatment with an ion exchanger or adsorbent) is necessary in order to ensure complete removal of the alkali metal catalyst from the alkoxylated starter compound.
The object of the present invention is accordingly to provide a process for production of long-chain polyether polyols without working up, in which oligomeric, alkoxylated starter compounds are first obtained from the low molecular weight starter compound (for example propylene glycol or trimethylolpropane) by an alternative catalysis to the conventional alkali metal catalysis, which oligomeric, alkoxylated starter compounds may then directly, i.e. without working up or removal of the catalyst, be further extended to yield long-chain polyether polyols by means of highly active DMC catalysts at very low catalyst usage rates (30 ppm or below).
German patent application No. 197 02 787.3 describes a process for the production of polyether polyols by catalysis with perfluoroalkyl-sulfonic acid salts (perfluoroalkyl-sulfonates) of the metals of group III A of the periodic system of elements (in accordance with the TUPAC convention of 1970).
It has surprisingly now been found that oligomeric, alkoxylated starter compounds having molecular weights of between 200 and 1000, which have been obtained by the metal perfluoroalkylsulfonate catalysts described in the above-stated German patent application from conventional, low molecular weight starters, such as for example propylene glycol or trimethylolpropane, by reaction with alkylene oxides at reaction temperatures of 80 to 200xc2x0 C. and catalyst concentrations of 5 to 200 ppm, relative to the quantity of the oligomeric, alkoxylated starter compound to be produced, may be converted directly, i.e. without working up and removal of the catalyst, by means of highly active DMC catalysts at very low catalyst usage rates (30 ppm or below) by reaction with alkylene oxides into higher molecular weight, long-chain polyether polyols. It this manner, long-chain polyether polyols may be produced entirely without working up.
It was also found that when the alkoxylated starter compounds obtained by catalysis with the metal perfluoroalkylsulfonates are used, the induction and alkoxylation times on DMC catalysis are distinctly reduced in comparison with the use of corresponding oligomeric starter compounds, which were produced by alkali metal catalysis and conventional working up.
By shortening the cycle times in polyether polyol production, reduced induction and alkoxylation times also improve the economic viability of the process.
The present invention accordingly provides a process for the production of long-chain polyether polyols without working up, in which oligomeric, alkoxylated starter compounds having molecular weights of 200 to 1000 are first obtained by catalysis with perfluoroalkylsulfonates of the metals of group III A of the periodic system of elements (in accordance with the IUPAC convention of 1970) from low molecular weight starters by reaction with alkylene oxides at reaction temperatures of 80 to 200xc2x0 C. and catalyst concentrations of 5 to 200 ppm, which oligomeric, alkoxylated starter compounds are then converted without working up and removal of the catalyst by means of highly active DMC catalysts at a catalyst concentration of 30 ppm or below, relative to the quantity of polyether polyol to be produced, by reaction with alkylene oxides into higher molecular weight, long-chain polyether polyols.
Catalysts used according to the invention for the production of the oligomeric, alkoxylated starter compounds are perfluoroalkylsulfonates of the metals of group III A of the periodic system of elements (in accordance with the TUPAC convention of 1970). This comprises the metals scandium, yttrium and the rare earth metals lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium. A further metal which may be used is xe2x80x9cmixed metalxe2x80x9d (also known as xe2x80x9cdidymiumxe2x80x9d), a mixture of rare earth metals obtained from ore.
Perfluoroalkylsulfonates are taken to be metal salts of perfluoroalkylsufonic acids, in which the metal is at least attached to a perfluoroalkylsulfonate group. Other suitable anions may also be present. Preferred compounds, are the metal salts of trifluoromethanesulfonic acid, which are known as trifluoromethanesulfonates or triflates. The following are preferably used: scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium triflate.
The perfluoroalkylsulfonates may be used individually or as a mixture.
The alkylene oxides used are preferably ethylene oxide, propylene oxide, butylene oxide and the mixtures thereof. Synthesis of the polyether chains by alkoxylation may, for example, be performed with only one monomeric epoxide or alternatively also randomly or blockwise with 2 or 3 different monomeric epoxides. Propylene oxide is particularly preferably used.
The low molecular weight starters used are compounds having molecular weights of 18 to 400 and 1 to 8 hydroxyl groups. The following may be mentioned by way of example: ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, dipropylene glycol, 1,4-butanediol, hexamethylene glycol, bisphenol A, trimethylolpropane, glycerol, pentaerythritol, sorbitol, cane sugar, degraded starch and water. The low molecular weight starters may be used individually or as a mixture.
The polyaddition catalysed by the metal perfluoroalkylsulfonates proceeds in the temperature range from 80 to 200xc2x0 C., preferably in the range from 90 to 180xc2x0 C., particularly preferably from 100 to 160xc2x0 C., at total pressures of 0.001 to 20 bar. The process may be performed without solvent or in an inert organic solvent, such as for example toluene, xylene or THF. The quantity of solvent is conventionally 10 to 30 wt. %. The reaction is preferably performed without solvent.
The catalyst concentration is in the range from 5 to 200 ppm, preferably from 5 to 100 ppm, particularly preferably from 10 to 50 ppm, in each case relative to the quantity of the oligomeric, alkoxylated starter compound to be produced.
The reaction times for the polyaddition are in the range from a few minutes to several days.
The molecular weights of the oligomeric, alkoxylated starter compounds produced by the metal perfluoroalkylsulfonates are in the range between 200 and 1000 g/mol, preferably in the range between 200 and 800 g/mol.
The polyaddition process may be performed continuously, in a batch or semi-batch process.
The oligomeric, alkoxylated starter compounds produced according to the invention may be directly, i.e. without working up and removal of the catalyst, further extended by means of DMC catalysts to yield higher molecular weight, long-chain polyether polyols. Highly volatile fractions are preferably first removed from the oligomeric, alkoxylated starter compound by distillation under reduced pressure (0.01-100 mbar) and at elevated temperature (50-150xc2x0 C.).
The two polyaddition stages may be performed separately (temporally and/or spatially, i.e. in different reaction vessels) or simultaneously as a so-called xe2x80x9csingle vessel reactionxe2x80x9d.
The highly active DMC catalysts to be used to produce the long-chain polyether polyols without working up from the oligomeric, alkoxylated starter compounds are known in principle and are comprehensively described, for example, in EP 700 949, EP 761 708, WO 97/40086 and in DE-A 197 45 120, 197 57 574 and 198 102 269.
The highly active DMC catalysts described in EP 700 949 which, apart from a double metal cyanide compound (for example zinc hexacyanocobaltate) and an organic complex ligand (for example tert-butanol), additionally contain a polyether having a number average molecular weight of greater than 500, are typical examples.
The alkylene oxides preferably used for the polyaddition are ethylene oxide, propylene oxide, butylene oxide and the mixtures thereof Synthesis of the polyether chains by alkoxylation may, for example, be performed with only one monomeric epoxide or alternatively also randomly or blockwise with 2 or 3 different monomeric epoxides. Further details may be found in Ullmanns Encyclopxc3xa4die der industriellen Chemie, English language edition, 1992, volume A21, pp. 670-671. Propylene oxide is particularly preferably used.
The starters used according to the invention are oligomeric, alkoxylated starter compounds having 1 to 8 hydroxyl groups, which have previously been produced from the above-stated low molecular weight starters by means of catalysis by the metal perfluoroalkylsulfonates without removal of the catalyst, and which have molecular weights of between 200 and 1000 g/mol, preferably of between 200 and 800 g/mol. The oligomeric, alkoxylated starter compounds may be used individually or as a mixture.
The polyaddition, catalysed by the highly active DMC catalysts, of alkylene oxides onto oligomeric, alkoxylated starter compounds containing active hydrogen atoms generally proceeds at temperatures of 20 to 200xc2x0 C., preferably in the range from 40 to 180xc2x0 C., particularly preferably at temperatures of 50 to 150xc2x0 C. The reaction may be performed at total pressures of 0.001 to 20 bar. Polyaddition may be performed without solvent or in an inert organic solvent, such as for example toluene, xylene or THF. The quantity of solvent is conventionally 10 to 30 wt. % relative to the quantity of the polyether polyol to be produced. The reaction is preferably performed without solvent.
The catalyst concentration is 30 ppm or below, preferably 25 ppm or below, particularly preferably 20 ppm or below, in each case relative to the quantity of the long-chain polyether polyol to be produced. The lowermost catalyst concentration is 0.1 ppm.
At these low catalyst concentrations, it is not necessary to work up the product. For use in polyurethane applications, it is possible to dispense with catalyst removal from the polyol without there being any negative impact on product quality.
The reaction times for the polyaddition are in the range from a few minutes to several days, preferably a few hours.
The molecular weights of the long-chain polyether polyols produced using the process according to the invention are in the range from 1000 to 100000 g/mol, preferably in the range from 1000 to 50000 g/mol, particularly preferably in the range from 2000 to 20000 g/mol.
Polyaddition may be performed continuously, in a batch or semi-batch process.
The highly active DMC catalysts generally require an induction time of a few minutes to several hours.
Using the oligomeric, alkoxylated starter compounds obtained according to the invention by catalysis with the metal perfluoroalkylsulfonates, brings about a distinct reduction (by approx. 25%) in the induction times on DMC catalysis, in comparison with the use of corresponding oligomeric, alkoxylated starter compounds which were produced by alkali metal catalysis and conventional working up (neutralisation, filtration, dehydration).
Simultaneously, using the oligomeric starter compounds produced by catalysis with the metal perfluoroalkylsulfonates, also substantially shortens the alkoxylation times on DMC catalysis (by approx. 50-60%).
This results in a shortening of the overall reaction times (sum of induction and alkoxylation times) of typically some 50%. In this manner, the shortening of cycle times in polyether polyol production improves the economic viability of the process.